Weird Low Speed Aux Fan Issue

[AWDBOB]

Hey R3V-

I installed a new genuine Aux fan in my ‘89 325i and am not getting low speed fan function.

Jumping green/black to black at the fan temp switch I hear the K1 relay click, but it does not engage low speed.

Jumping brown/black to black engages high speed and works fine.

Pressing snowflake inside the car the low speed fan does not engage and I get no voltage at pin 86, but with the K1 installed I DO get relay click, which seems counter intuitive to me. Should get no relay click if I don’t have power at pin 86 with snowflake depressed…..

Also with snowflake engaged I get blower fan, which I thought was only supposed to happen with the recirc button engaged. Tested two A/C switches with the same results.

Do I have an HVAC wiring issue? An Aux fan resistor issue?

halp

[reelizmpro]

Did you install the old resistor into the circuit correctly? Check to see if the resistor itself is still good, then check the wiring, etc.

[AWDBOB]

Did you install the old resistor into the circuit correctly? Check to see if the resistor itself is still good, then check the wiring, etc.

The no power at pin 86 with snowflake engaged is the one that threw me for a loop because that technically means the HVAC wiring isn’t sending signal out to the K1.

But I have good constant power at pin 85.

[ghrays]

This may be immaterial but I had an issue whereby the aux fan only intermittently energized when the AC button was activated. The temperature switch at the upper radiator was OK as were the relays in the fusebox and the fan resistor.

When I checked for voltage with a multimeter at the body harness connector to the fan, and 12V would appear when activating the AC switch. I finally determined it was a failure of good connection between the body harness connector and the fan harness connector (near the driver's side headlight). There was corrosion in the female harness connectors. By replacing the three watertight female connectors (I believe part number 61130007442) the fan now works flawlessly.

[AWDBOB]

Good info ghrays!

Unfortunately I am just an idiot and was led astray in my diagnosis by the weird pin 86 thing noted above.

I ignored that and focused diagnosis on the low speed resistor and it turns out that was bad despite being replaced recently.

Problamo solved

[reelizmpro]

Glad you got it sorted quickly Bob. We can't assume anything when diagnosing electrical problems on 30+ year cars. I went through it all on my E30's. No visible corrosion but it was enough to not make good contact. I was thinking I had an internal break in the fuse box, etc. I've battle fan issues on my M3's for some time and finally figured out what was happening. On the M3, the aux fan switch faces downward at an angle on the thermostat housing, close to the exhaust. Why is this an issue? Well for one you cannot see the switch terminals once installed and the heat deteriorates the rubber insulation in the connector. Each time you remove/install that connector you risk pieces of rubber breaking off and falling inside blocking the female terminals from making contact. Since the switch is on the thermostat housing, it also sees vibration from the buzzy S14. I've never had this issue on the 325i because the switch is located a lot higher (on the radiator) and mounts in a horizontal position so the connector/aux switch doesn't see as much heat or vibration.